Michal Vyskocil <mvyskocil@suse.cz> writes:
> I like such idea - but how hard would be to add a config options to
> extend a list of default headers used for indexing?

Not hard.

Obviously, notmuch is already indexing some headers, (From, Date, To,
Subject), and it wouldn't be hard to index more. [*]

List-Id has been proposed often enough that it should probably be on by
default.

Then, there are other, slightly more special-case headers, (like headers
added by spam filtering software), that probably would be best added on
an opt-in basis based on a configuration option.

-Carl

[*] The existing set of indexed headers is really just historical
accident based on two things:

1. I was originally writing index code to match sup's index building, so
   I focused on the headers sup indexed.

2. I wrote code to index enough headers to satisfy my use case.

It's embarrassing to me that I added this note to the notmuch TODO file
in October 2009 (and it's still there):

    Add support for the user to specify custom headers to be indexed.

-- 
carl.d.worth@intel.com